HDLC
(High Level Data Link Control, HDLC) , .
HDLC (Synchronous Data Link Control Protocol, SDLC), IBM , . ,
1993 ISO HDLC (ISO 3309, 4335, 7478 ..) , X25 (Link Access Procedure, LAP) IP- (PPP), (Link Access Procedure Balanced, LAPD) , , ( LLC IEEE 802.3).
: , , .
, HDLC , . ; ; , . . , . , (.4.33).
, , , , . , .
1. (Normal Response Mode, NRM) -. , , (); , . .
2. (Asynchronous Response Mode, ARM) NRM , (, ), , , . , , , , , , , . , NRM ARM (. 4.34), . , .
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3. (Asynchronous Balance Mode, ABM) . . , , .
HDLC (.4.35) .
8- - 01111110 (). , . 1, . 1, 0; 0, , . , . , , , .
HDLC () (abort), . . , , .
(8 ) , , . - , , . (NRM ARM) ; ABM , .
HDLC : (I-), (S-) (U-). ( ); , . . 4.36.
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0; 10 11 , .
"" P/F (Poll/Final). (NRM, ARM) , 1 P/F, ; ( ) 0, 1. (ABM) 1 , .. , ( ARQ).
HDLC ARQ, - . N(S) ( ARQ); N(R) , "" (). N(S) N(R) 3 ; ARQ N , ARQ - . 16 , - 7 . , 0 127 63.
SS ( Type) :
SS = 00 | (Receive ready, RR); N(R)-1. |
SS = 01 | (Reject, REJ), NAK; , N(R); (Go-To- Back N). |
SS = 10 | (Receive not ready, RNR). N(R)-1 ( , ). . |
SS = 11 | (Selective reject, SREJ). , N(R) ( ) . ARQ . |
, , . , SNRM (Set NRM) SABM (Set ABM) ( , ) ; SNRME SABME ; UA (Unnumbered Acknowledgement), FRMR (Frame Reject). DISC (Disconnect). , , ( M . 4.36), 32 /; . , .
, , .
16- 32- FCS (Frame Checking Sequence) , CRC, , .
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4.37 , . 4.38. .
A SABM, , ( ). UA . "", . ( ) , DISC, , UA, .
I-, , , (RR RNR) , REJ . , , .
HDLC , 3- , . , . , , HDLC. (, Cisco) ; HDLC, , PPP.
, - . (); -. , , , . , . Point-to-Point Protocol (), , . SLIP (Serial Line Internet Protocol).
SLIP
Serial Line Internet Protocol 1984 . (Rick Adams) SUN . RFC 1055. - - IP . TCP IP , . .
, ;
IP ; , Internet , ;
;
.
IETF (Internet Engineering Task Force) Point-to-Point Protocol (), RFC 1661, 1662,1663 ( 40) .
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PPP-
Point-to-Point Protocol , , . :
( Link Control Protocol, LCP),
( Network Control Protocol, NCP).
, (LCP NCP), PPP .
(.4.39) HDLC. HDLC-. , PPP, HDLC, - . , (ESC-), 1 ; ESC-, .
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, , 1, ( ).
11000000, .. HDLC. , ( IP ). , HDLC (RFC 1663). HDLC, .
, , , (IP, IPX ..), .
CRC CCITT-16 CCITT-32.
PPP- , LCP-, NCP-. , - LCP (0xC021) NCP (0x8021). LCP , . 4.6 RFC 1661 LCP-. Ȼ , λ - . , , Echo Discard, .
4.6
/ | |||
Configure-Request | à | ||
Configure-ACK | ß | ||
Configure-NAC | ß | ||
Configure-Reject | ß | ||
Terminate- Request | à | ||
Terminate- ACK | ß | ||
Code-Reject | ß | ||
Protocol- Reject | ß | ||
Echo- Request | à | ||
Echo-Replay | ß | ||
Discard-Request | à |
"-" PPP, LCP, . , . PPP NCP . , PPP. , LCP NCP , ( , ).
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IP- . 4.40. , . 4.37; LCP; - Password Authentication Protocol (PAP), Challenge-Handshake Authentication Protocol (CHAP). NCP-. , , . , IP-, NCP IP- IP-.
PPP (RFC-1990). (MP - MultiLink Protocol).
, PPP HDLC- . , , , , HDLC ARQ (RFC 1663).
PPPoE (Point-to-Point Protocol over Ethernet). Ethernet (. 4.41) , , , , . Ethernet , , PPP . , PPPoE, PPP, ( Ethernet) (, , , ).
PPPoE Ethernet , . 4.42. 1; 4- 0x1 PPPoE.
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8- PPPoE. ( ) PPP (.4.43). - , . PPPoE- PPPoE- Ethernet- 0x8863; PADI (Active Discovery Initiation) PPPoE, 0x09 PPPoE. PPPoE-, , PADO (Active Discovery Offer, 0x07), . , , - . PADR (Active Discovery Request 0x19) . PADS (Active Discovery Session-confirmation, 0x65), 16- ; PPPoE , . , , .
PPPoE- PPP : , , (MTU), . PPPoE- PPP AAA (Authentication, Authorization, Accounting) . PPP .
PPP-over-Ethernet . Ethernet- PPPoE Protocol Ethernet (08863 08864 - . , ( , , PPPoE- ..), (), ", , ", , , 2 , 2 , .
Ethernet Header
SrcAdr: 00:50:da:42:d7:df,
DstAdr: ff:ff:ff:ff:ff:ff
Protocol: 0x8863 (Discovery Stage) 0x8864 (PPP Session Stage).
PPoE Header
Version (4b): 1
Type (4b): 1
Code (8b): Active Discovery Initiation (0x09)
Session ID (16b): 0000
Payload Length (16b): 24
PPoE Payload
(Discovery Stage)
PPPoE Tags
TagType: Service-Name { }
TagType: Host-Uniq (16 b)
TagLenght: (Binary Data, 16 b) - { TagValue }
TagValue: 11000111 01011100
(PPP Session Stage)
PPP PROTOCOL-ID = 0xc021 (2 bytes) - IP-
PPP payload (<= 1492 bytes)
"Service-Name" , . TagLenght , . "Host-Uniq" (PADO c PADI). "TAG VALUE" , ; .
, MTU PPPoE 1492 , 1500 , Ethernet. 8 : 6 - PPPoE 2 - PPP ( , ).
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:
, ..
,
,
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- HDLC.
o (01111110) .
o , ESC-, .
o .
PPP, HDLC, .